Wi-Fi is a Passion


Site Survey tools and process

For good site surveys you need also tools, hardware, and software. Tools that can be used during a site survey are protocol analyzers and spectrum analyzers. I go into deeper detail on those tools in previous blogs.

When we look into the protocol analyzer, you need an adapter that can capture the packages. This adapter needs to support the PHY, because you cannot capture 802.11n frames with an 802.11g adapter. Same for an adapter that supports 2 streams—you cannot capture 3 streams. Vice versa is possible, so it is backwards compatible. Protocol analyzer programs make the packages visible and readable, and it is possible to put some filters on it so you will see some nice graphs based on the frames. For example, Omnipeak has some graphs for top ten talkers or percentages of which protocol you will see the most. There are color schemes in which every type of frame has another color so it is organized. During site survey, you can use a protocol analyzer for example, to identify the wireless networks or look for areas with a high frame retry. More information about protocol analyzers can be found in this blog that I wrote during the preparation of my CWAP exam: Protocol Analysis.

Spectrum analyzer can be used for finding interferences. This is needed for deploying wireless in a new or existing environment. There are non-Wi-Fi devices that use the same spectrum and because of that it might be smart not using those channels around that device. To find those devices a spectrum analyzer will help you. More information about spectrum analyzers can be found in this blog that I wrote during the preparation of my CWAP exam: Spectrum Analysis.

Site survey software is the software that can be used for predictive planning or walking through the building for measuring or validating the existing network. It shows the RSSI, SNR, data rates, and more. There are tools that can, based on the requirements, tell where the network is healthy or not healthy and what might cause the problems. Before doing a site survey, you must import the blueprints/floorplans of the location and calibrate it. There are certification tracks in the specific site survey tools like Ekahau and AirMagnet.

Other tools that might be helpful to use during a survey are throughput testers. There are command line tools or throughput testers with a graphical interface. A common tool is iPerf. What this tool does is it sends a file (upstream and downstream) in which you can specify the payload to the server. The server can be a server or just a laptop or even smaller, like a raspberry pi / odroid type of device.

You can use tools like inSSIDer, Kismit, or Wi-Fi explorer (MacBook only) for seeing the different types of networks. Those tools capture the beacon frames and show the information like SSID name, BSSID, signal strength, and security type.

These are tools that are needed for a good survey, both software and hardware. However, there is more that you need to take with you. A laptop or tablet where the site survey tool is installed on, extra batteries, since the battery of the laptop is not endless, and as well, when you are using the AP on a Stick approach, an access point. You should use the access point that you are going to deploy with the same settings. Doing a site survey with 100mW and deploying the access points at 50 mW will change the coverage. In addition to access points, for some sites it is necessary to have also one or more types of antennas with you. For example, a semi-directional antenna. This can be used in High-Density areas to direct the signal in the direction where the clients are and minimize CCI. Another type of antenna is an omni-directional antenna with a higher gain than the internal omni-directional access points. High-gain directional antennas are helpful with outside surveys. Point-to-point connections are an example of this.

Those tools, software and hardware, are wireless related. There are a lot of helpful tools you’ll want to take that make your life easier during a site survey. I mentioned already the extra battery pack for your laptop, but you also need a PoE battery for your access point in combination with a UPS since you want to survey for a day and may not always be close to wall outlets. You will want to take CAT 5 or CAT 6 cables to connect the access point to the PoE injector. It is also possible to simulate the variable-loss by a variable-loss attenuate device. You need those devices when you want to simulate a behavior that you cannot simulate with just the access point and antenna. Again, those are still network related tools. What about binoculars? Sometimes access points are hanging 30+ feet high, and you want to read the sticker on the access point. When you are working with a co-worker, you’ll want a phone or walkie-talkie to communicate with him or her over distance.

As said earlier, one of the first things you need to do in a site survey tool is calibrate it. For this you need a tape measurer or a tool based with laser to measure distance. During the survey, you decide where the access points need to deploy; however, most of the time you are not the one who is deploying those access points. For this it will be helpful to have a photo camera or (colored) tape to mark the location, as well as fastening ties, duct tape, or other items for temporarily positioning access points on a spot for measurement.

With a site survey, you need to walk long distances, and if you use an AP on a Stick solution, you need to take the APoS with you. To make it easier you can use a rolling cart, but keep in mind the material the cart is made from. If you pick a metal cart to put the AP on a Stick on, metal can reflect the RF propagation and this will affect the survey. The last tool that I will mention here is the GPS unit for outside surveys. There are site survey tools that have the ability to use a GPS unit for the exact location. In this scenario, you can drive around in a car and the GPS unit tells the software the position of where you are. This helps to cover bigger outdoor sites.

It is important to acquire the floor mappings, know where the building’s inventories are and from what materials they are made, and the same for the building’s construction material, office layout, and people density areas. Those plans show a lot of information about the area, such as where the wired closets are and elevators where the internal and external walls are. This gives you a good idea of the building. Those plans are not only good for you, but also for the documentation. You can direct the people, who will deploy the wireless network, where to deploy the access point by pointing it out on the map. Together with some photo or by marking the location with tape, the engineer who deploys it knows exactly the right spot.

The building material gives you an idea of how RF propagation might propagate. Also, cabinets, racks, warehouse shelves, and other storage can influence the RF drastically. If it is a changing environment with warehouse shelves that are one day full and the next day empty, how do you design for that? A rack full of metal parts in an auto storage sure would affect the RF. Lead-lined walls in hospitals or in food court areas where a lot of microwaves are, would definitely affect the RF in a bad way. In environments with high reflective materials there is an option to disable short guard interval.

Also, something that is part of the process of site surveys is getting access to the location. Most buildings you need a batch to get in different types of rooms. This may be a special key or even a supervisor who shadows you during the whole location. Not only is permission for rooms sometimes required, when deploying wireless networks in buildings more than 200 feet high (in the USA), you need special permission from the government. This is because of interference with aircraft communication. An exception to this rule is if there are already taller buildings around. The closer you get to an airport, the stricter rules can be applied.